This project consists of a three-year program of research into the functioning of the voice source in speech and singing. The research can be divided into five areas, summarized as follows: (1) Our investigation of the influence on voice quality of acoustic interaction between the glottal source and the supraglottal vocal tract will be continued, using mathematical analysis supported by measurement of glottal air flow, obtained by inverse-filtering oral air flow, vocal fold contact area, as measured with an electroglottograph, and subglottal pressure, obtained by extrapolating between oral pressure peaks during adjacent unvoiced bilabial stops. (2) Using the same techniques as in (1), a theoretical and experimental investigation of breathy-voice will be continued, to determine the relationships between the various types of breathiness and source-tract acoustic interaction. Breathy-voice will also be used to measure vocal tract inertance at low frequencies. (3) A theoretical and experimental analysis of the electroglottograph will be continued. (4) The effect of transglottal pressure on vocal fold action will be measured through the use of forced variations in supraglottal pressure. (5) A pilot study will be made of glottal adduction-abduction movements during voicing in the speech of normal and deaf speakers, to explore the possibility of using the easily measured /h/ sound as a test of competence in voiced-unvoiced contrasts, and in speech training.